Yeast and the AIDS Virus: The Odd Couple Abstract Despite being simple eukaryotic organisms, the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe have been widely used as a model to study human pathologies and the replication of human, animal, and plant viruses, as well as the function of individual viral proteins. The complete genome of S. cerevisiae was the first of eukaryotic origin to be sequenced and contains about 6,000 genes. More than 75% of the genes have an assigned function,